Scientist wants to perform a controlled experiment to test the effect of rust on chemically treated iron. which action would be most important to perform in a controlled experiment?

It seems that you have missed the necessary options for us to answer this question, so I had to look for it. Anyway, here is the answer. If a scientist wants to perform a controlled experiment to test the effect of rust on chemically treated iron, the action that would be most important to perform in a controlled experiment is this: Test a piece of treated iron and a piece of untreated iron under the same conditions. Hope this helps.